The present invention relates to an electric rice cooker and, more particularly, to an electric rice cooker which automatically controls the proper end time of heating for cooking in accordance with the actual temperature inside a cooking pot or kettle containing rice and water.
A conventional electric rice cooker has a magnetic shunt steel member mounted at the outer bottom surface of the cooking pot or kettle and a permanent magnet attracted and held to the magnetic shunt member against an urging force of an elastic member such as a coil spring. The temperature of the cooking kettle heated by an electrical heater can be constantly detected by the magnetic shunt steel member as cooking progresses. When the detected kettle temperature reaches a predetermined "cooking complete" temperature or "cooked" temperature, the permeability of the magnetic shunt steel member is abruptly decreased. The attraction force between the permanent magnet and the magnetic shunt steel member then becomes smaller than the urging force of the coil spring. As a result, the permanent magnet is detached from the magnetic shunt steel member by the urging force of the spring. Upon this movement of the permanent magnet, the cooking heater is deenergized, thereby completing the cooking operation of the electric rice cooker. Thus, deenergization of the cooking heater is performed by mechanical action of the permanent magnet.
In the conventional electric rice cooker having the switching mechanism described above, the time at which the cooking heater goes OFF, that is, the proper cooking end time, cannot be uniformly set for all mass-produced electric rice cookers, due to variations in various characteristics of the magnetic shunt steel member, the permanent magnet and the coil spring, as well as in the attraction state between the magnetic shunt member and the bottom of the cooking kettle. Therefore, the precision of the "OFF" time is undesirably arbitrary for each individual rice cooker. Individual mass-produced rice cookers may have such a delayed heater "OFF" time that the cooked rice actually burns. On the other hand, another rice cooker may have a premature "OFF" time, so that the necessary conversion of beta-starch into alpha-starch cannot be completed. As a result, in either case, good-tasting cooked rice cannot be obtained.